The Industrial Scientific Medical (ISM) frequency band can be used for wireless communication of data. One communication standard specifying the ISM frequency band for operation is the Bluetooth standard. Another communication standard specifying the ISM frequency band for operation is WLAN (Wireless Local Area Network), e.g. according to IEEE standard 802.11b.
Transceivers adapted according to different communication standards but being operative in a single frequency band may be provided in a single wireless communication apparatus. The wireless communication apparatus may sometimes be relatively small, such as a mobile telephone. If the wireless communication apparatus is relatively small, the transceivers will be located in relatively close proximity. Thus, antennas for the two transceivers will also be located in relatively close proximity. When the transceivers are located in close proximity, they will be sensitive to all incoming signals independent of channel. Thus, the transceivers must process all incoming signals in the frequency band of interest. This could desensitize or block the RF front-ends of the transceivers.
One approaching to avoiding such problems is the Medium Access Control (MAC) sub-layer based Packet Traffic Arbitration (PTA) scheme. PTA implements a control supervisor that acts like a time division traffic controller between WLAN and Bluetooth MACs. The control supervisor controls that each MAC protocol uses a handshake mechanism to authorize transmission before actually sending out information. One problem with the PTA scheme is that it suits asynchronous traffic from both Bluetooth links and WLAN links, but fails to accommodate synchronous or time-critical types of data traffic and applications, e.g. from the Bluetooth transceiver. Synchronous data traffic and time-critical data traffic are generally prioritized data traffic, i.e. the audio data packets should be delivered within a predetermined time period. Prioritized data traffic may e.g. include voice, audio, video or file data.
One situation where problem could occur due to Bluetooth-WLAN coexistence is simultaneous transmission of voice, which is prioritized audio data traffic, over a
Bluetooth link and asynchronous TCP (Transmission Control Protocol) traffic, such as emailing and Internet access, over a WLAN link. The prioritized data traffic may be transmitted over a Bluetooth SCO (Synchronous Connection-Oriented) link using HV3 packets. The TCP traffic may be transmitted over a WLAN link as specified e.g. in IEEE 802.11b or 802.11g. Using the SCO link, the Bluetooth transceiver will be active during 1.25 ms (milliseconds). Then, the Bluetooth transceiver will be inactive for 2.5 ms, leaving a window during which the WLAN transceiver may be active before the Bluetooth transceiver is active again.
Typical frame exchange durations of WLAN 802.11b are listed in the table of FIG. 1. As can be seen from FIG. 1, the total frame exchange duration may under certain conditions exceed the time period during which the Bluetooth transceiver is inactive when an SCO link is used.
This is e.g. the case if the PHY (PHYsical channel) rate is 5.5 Mbps or less, wherein the frame exchange duration may be 2.695 ms or more depending on PHY rate. Thus, the MAC layer frame exchange will not be finalized during the inactive period of the Bluetooth transceiver. As the traffic over the SCO is prioritized, the Bluetooth transceiver will start transmit or receive at the next active period, which may cause the problems mentioned above due to simultaneous transmission by the Bluetooth transceiver and the WLAN transceiver.
Another situation where problem could occur due to Bluetooth-WLAN is transmission of Bluetooth Advance Audio Distribution Profile (A2DP) data traffic and asynchronous WLAN TCP data traffic. The A2DP data traffic is prioritized data traffic and could be communicated using a Bluetooth ACL link and DH5 packets. With an ACL link, the Bluetooth transceiver will be active for 3.75 ms, and inactive for 3.75 ms before it is active again. As can be seen from FIG. 1, this could cause problem when the PHY rate is 2 Mbps or less, wherein the frame exchange rate may be 6.636 ms or more depending on PHY rate.
If a PTA scheme is used, there can be further consequences if the frame exchange duration of the WLAN traffic exceeds the time period, during which the Bluetooth transceiver is inactive. Firstly, the lower PHY rates are normally used for access from longer distances or at the edge of a cell. Thus, any device using the PTA scheme may lose a WLAN link to the access point if prioritized Bluetooth traffic is communicated. Secondly, for any reason when the WLAN transceiver cannot get its MAC ACK (ACKnowledge message) back after a few retries, its auto-rate-fallback mechanism will switch the transmission rate to a lower one. This will obviously worsen the situation. The transmission rate will thus be further reduced until the lowest basic transmission rate is reached. Finally, the device containing the Bluetooth transceiver and the WLAN transceiver will be disconnected. Consequently, the PTA scheme will not solve the co-existence problem between prioritized BT traffic and asynchronous WLAN traffic. In such a case, only the Bluetooth communication is guaranteed.
A further solution to some of these problems may be provided by a MAC layer approach. However, a MAC layer approach would require that certain modifications be made to access points that are already deployed, such as in hotspots.